A variety of techniques have been developed in which tissues or organs in a patient's body are heated or cooled. Tissues may be heated by a variety of techniques, including high frequency ultrasound, radiofrequency treatments, laser treatments, use of infrared radiation, and by direct application of thermal energy. Cooling is often effected cryogenically. Techniques that heat and cool tissues may be collectively referred to as “thermal techniques.”
Thermal techniques are useful for diagnosing a variety of disease states and for treating a variety of disease states. More specifically, thermal techniques may be used to diagnose and/or treat cancerous tissues, to destroy diseased tissues, to congeal blood, and to perform a variety of other diagnostic and surgical procedures. Examples of organs that may be subjected to thermal techniques include the heart, the lungs, gastrointestinal organs, the liver, the pancreas, urological organs, prostates, reproductive organs, and skin.
The degree of heating or cooling that is required to optimize the efficiency of some thermal techniques may adversely affect tissues or organs that are adjacent to a treated tissue or organ. For example, a great deal of heat is generated when left atrial ablation techniques are used to treat atrial fibrillation in human subjects. In addition to heating and treating the diseased tissue in the heart H, the esophagus E, which is adjacent to the left atrium LA of the heart H, as shown in FIG. 1, may also be heated. As FIG. 1 illustrates, a typical human esophagus E typically has a narrow oval shape that resembles a pancake, with a large portion of the outer surface of the esophagus E located next to or in contact with the left atrium LA, although the size, shape, and/or position of the esophagus E may vary. In an average human adult, about 58 mm of the length and the majority of the front side of a 14 mm diameter esophagus E is located in proximity to or contacts the left atrium LA. As a consequence of this intimate arrangement between the esophagus E and the left atrium LA, the heat generated during left atrial ablation may damage the esophagus E and may, in some cases, create an esophageal fistula. Unfortunately, the complications that arise from esophageal fistula often do not present themselves until weeks after the procedure and, in many cases, at too late a time to treat and/or cure the sometimes fatal damage that has been done.
In recognition of the potentially dire consequences of overheating the esophagus E during left atrial ablation, some physicians have started using catheters with single temperature sensors to monitor the temperature within the subject's esophagus E. Typically, a catheter with a size of 9 French (about 3 mm diameter) to about 18 French (about 64 mm diameter) is used in conjunction with a conventional temperature sensor (e.g., an esophageal stethoscope available from Smiths Medical of Hythe, Kent, United Kingdom). If the sensed temperature reaches a predetermined level, the physician may discontinue the left atrial ablation momentarily to allow the esophagus E to cool. The effectiveness of these techniques is limited, however, as a single temperature sensor may only monitor heat at a single location within the relatively large area of the esophageal wall located adjacent to the left atrium LA.
In an apparent effort to reduce the likelihood of esophageal fistula during left atrial ablation procedures, a variety of different types of inflatable devices have been developed. Some inflatable devices are configured to cool the esophagus E during left atrial ablation. Other inflatable devices are configured to ensure contact between one or more temperature sensors and the interior surface of the front of the esophageal wall. Despite assertions to the contrary, since the esophagus E is confined between the left atrium LA of the relatively rigid heart H and the even more rigid vertebral column VC (see FIG. 1), any change in the shape of the esophagus E by inflating a device that has been introduced into the esophagus E merely pushes or distends the esophagus E closer to, or into more intimate contact with, the left atrium LA. The obvious result of such movement or distension is an increase in the likelihood that a left atrial ablation procedure will cause an esophageal fistula. In addition, use of an inflatable device will undesirably prevent a subject from swallowing during the typically lengthy (two to four hour) procedure, which may unnecessarily require that the subject be placed under general anesthesia during the procedure.